Edema in a tissue, for instance lymphoedema, vein-related edema or also edemas born in muscle injuries are a problem that usually is treated by using compression products such as compression stockings or compression gloves. In dimensioning the compression products, determining a suitable compression pressure is a problem.
One method to measure an edema is based upon palpating by hand or fingers and measuring with a tape measure. In some measuring devices based upon state of the art, pressure is applied upon the tissue with a mechanical presser, whereupon the mechanically produced force is measured and the change in the edema or the edema pressure is calculated based upon this. In some, the solutions based upon state of the art are bio-impedance-based devices for measuring the tissue fluid status as well as invasive pressure probes to be inserted into the tissue.
In the U.S. Pat. No. 5,484,399 there is presented a method and device for reducing tissue pressure. The device also comprises a tissue pressure meter. The device has needle-like, long tubes, in the sharp end of which there is at least one hole.
The device is pushed into the tissue and air is sucked from the tubes, whereupon the fluid pressure in the tissue exceeds the pressure in the pipe. Thus fluid is transferred from the tissue into the tube and the pressure in the tissue decreases. The tissue pressure meter is situated in one of the tubes.
In the FI patent 109651 there is presented a method for measuring tissue pressure. In the method an electromagnetic sensor is attached upon the surface of the skin, whereupon the capacitance of the sensor is proportionate to the dielectric constant of the skin and the subcutaneous tissue, which in its turn is proportionate to the water content of the skin. The edema is determined by measuring the capacitance of the electromagnetic sensor at a high frequency, such as 20-500 MHz.
In the U.S. Pat. No. 6,186,962 there are presented methods and devices for measuring tissue pressure. In one device according to the invention there is a platy component, which is attached to the tissue. In the disc there is an aperture for a rod, which is pushed towards the tissue, whereupon the tissue pressure is deducted from the forces directed to the rod.
The above presented measuring methods of the devices according to the state of the art include uncertainty factors, such as the interface between the skin and the electromagnetic sensor and the natural fluctuation in tissue water content. In addition, measurements may be extremely uncomfortable for the patient, as for instance the mentioned invasive methods.
The aim of the present invention is to offer a method and a device for defining tissue pressure in a non-invasive way, utilizing the tissue's own pressure and elasticity.
Characteristic for the tissue measuring device according to the invention is that the device comprises a pressure chamber, means for measuring the pressure in the pressure chamber and means for measuring the rising of the skin tissue caused by the negative pressure.
A device according to an embodiment comprises in addition a CPU, which comprises the means for processing and saving data.
A device according to a second embodiment comprises in addition a pressurization unit, which has been arranged in order to achieve negative pressure in the pressure chamber.
A device according to a third embodiment comprises in addition means for determining tissue pressure by means of the measured skin tissue rising and the measured pressure in the pressure chamber. The measured skin tissue rising and/or the pressure chamber pressure can also be measured as a function of time in order to determine tissue pressure.
In a device according to a fourth embodiment, the means for measuring the rising in skin tissue comprises at least one range sensor. The range sensor may for instance be an infrared sensor, a laser sensor or a tonometer. The device may in addition have means for measuring blood pressure and/or imaging subcutaneous tissues.
The tissue pressure measuring method according to the invention is characterized in that the method comprises the stages in order to create a negative pressure on the tissue surface, to measure the said negative pressure, to measure the tissue rising caused by the negative pressure, and to determine the tissue pressure on the basis of the measured negative pressure and the measured tissue rising.
In an embodiment of the method the negative pressure and/or the tissue rising is measured as a function of time in order to determine tissue pressure.
An advantage with the method lies in that it is non-invasive and that no electrical current or magnetic field is introduced into the tissue. There is created a negative pressure on the skin or tissue surface, whereby the own internal pressure in the tissue and the elastic properties of the tissue are utilized. It is also possible to utilize positive pressure or a combination of positive pressure and negative pressure in the measurement.